Transparent zinc oxide thin films that are doped or undoped with group IIIB elements and have high visible light transmittance are employed in a broad range of applications such as photocatalytic films, UV-cutting films, IR-reflecting films, the buffer layers of CIGS solar cells, the electrode films of dye-sensitized solar cells, antistatic films, compound semiconductor light-emitting elements, and thin-film transistors.
A variety of methods of manufacturing doped or undoped transparent zinc oxide thin films are known (Nonpatent Reference 1). The chemical vapor deposition (CVD) method (Nonpatent Reference 2), spray thermal decomposition method (Nonpatent Reference 3), spin coating method (Patent Reference 1), dip coat method (Nonpatent Reference 4), and the like are typical known coating methods employing starting materials in the form of organic zinc compounds.
However, the chemical vapor deposition (CVD) method presents various problems such as high manufacturing costs due to the necessity of using a large vacuum vessel and due to an extremely slow film formation rate, and does not permit the formation of large items because the size of the zinc oxide thin film that can be formed is limited by the size of the vacuum vessel.
The above coating methods afford more convenient apparatuses and achieve higher film formation rates than the chemical vapor deposition (CVD) method, thereby affording higher productivity and lower manufacturing costs. Moreover, since they are not limited by the vacuum vessel because there is no need to employ one, they afford an advantage in that large zinc oxide thin films can be produced.
In the spray thermal decomposition method, the solvent is dried simultaneously with the spray coating, after which the substrate temperature is raised to 360° C. or higher to obtain a thin zinc oxide coating.
In the above spin coating and dip coating methods, the solvent is dried following spin coating or dip coating, after which a thin zinc oxide coating is obtained by raising the substrate temperature to 400° C. or higher.